Two layer diagonal decking for wooden bridges

ABSTRACT

A deck for wooden bridges that consists of two layers ( 3  &amp;  4 ) attached to bridge structural members ( 1 A &amp; 1 B,  2 ) using traditional attachment methods ( 5 ). Having the first layer fastened to bridge support members in an oblique angle. With the second layer on top of the first layer and attached through first layer to bridge support members in the opposite oblique angle from the first layer.

BACKGROUND

1. Field of Invention

This invention relates to wooden pedestrian and vehicular bridges.

2. Description of Prior Art

Timber bridges have been constructed by humans since prehistoric times, one of the oldest on record was built in 783 B.C. over the Euphrates River in Babylon, wooden bridges have played a significant part in human civilization ever since. About 2000 years ago Roman armies erected timber bridges to march their troops across rivers for the expansion and control of their empire. In more recent history, the timber bridge was instrumental in the modernization of this country. From 1797 until 1860 the U.S. Patent Office issued 51 patents for timber bridges. Some of the more famous were the Town's lattice truss patented 1820, Long's truss bridge patented 1830, the Howe truss patented 1840, and the Pratt truss patented 1844.

These bridge designs, as well as most others were primarily concerned with greater spans and more load bearing capacity, with minimal interest in lateral strength. The first reference I discovered to “lateral sway” was in a patent issued to John P. Avery, U.S. Pat. No. 33629 issued Nov. 5, 1861, for a truss design that helped prevent lateral sway. About the time this problem was beginning to be addressed in timber bridges the use of steel began to compete with wood as a bridge building material. Hence the problem of lateral weakness in timber bridges was not, in my opinion satisfactorily resolved.

As timber bridges continued to be constructed well into the 20^(th) century, the designs were virtually unchanged from the mid-19^(th) century on. A reference to the lateral instability of these common timber bridges is found in a book titled: “Covered Bridges Of The West” by Kramer Adams, copyright c1963, Library of Congress Catalogue Card No. 63-19906. On page 50, Reverend Art Guenther of the Apache Lutheran Mission says: “can remember when he and his young Indian friends used to get the sturdy old White River covered bridge “swaying like a hammock” by carefully timed group running back and forth”. It's little wonder that a flood destroyed this bridge. If children playing could make it “sway like a hammock”, what chance would it have against a rain swollen river?

With the advent of glue laminated lumber, the timber bridge is experiencing a revival in modern times. Lateral strength is intrinsically greater in this type of bridge over its wooden predecessors, since the decking is typically large glue-laminated panels doweled together. But for those desiring the esthetics, or nostalgia of the traditional timber bridge the inherent weakness is still present.

OBJECTS AND ADVANTAGES

Accordingly, the objects and advantages of my invention are:

-   -   (a) to provide a traditional timber bridge with superior lateral         strength, testing showed a 400%-800% increase in lateral         strength over the two common decking methods;     -   (b) to provide an integral design that increases strength         without awkward members, like “flying buttresses”;     -   (c) to provide the greatest rigidity with the least amount of         material, by using the deck as the lateral bracing members;     -   (d) to provide a bridge that can be pre-assembled and have the         strength necessary to be lifted or drug into place without         structural damage;     -   (e) to provide a bridge that has a far greater resistance to         failure due to catastrophic events, such as wind, flood, and         earthquake.

DRAWING FIGURES

FIG. 1 shows a bird's eye view of deck attached to bridge support members.

FIG. 2 shows an end view of the deck and beams at eye level.

REFERENCE NUMERALS IN DRAWINGS

-   -   1A & 1B typical beam, stringer, or truss chord     -   2 cross beam     -   3 bottom layer diagonal decking     -   4 top layer diagonal decking     -   5 common fasteners, such as bolt, screw, spike, dowel, etc.

SUMMARY

A decking method for wooden bridges comprised of two layers of decking installed in an oblique angle to the main structural support members, with one layer in the opposite oblique angle from the other.

Description—FIGS. 1&2

The typical embodiment of the invention as shown from above (FIG. 1), attached to any bridge support members of the common type constructed by those skilled in the art. Where in parts 1A & 1B are beams, stringers, or truss chord members, part 2 is any typical configuration of cross brace members, perpendicular to the main beams. Parts 3 & 4 are the two layers of diagonal wood decking fastened to the main supports by part 5. FIG. 2 is an end view at eye level showing the end grain of the main support beams (parts 1A&1B), part 2 is the cross beam with the two layer diagonal decking (parts 3 & 4) attached on top.

Operation

The function of two layer diagonal decking is to strengthen bridges laterally, and therefore gain overall strength and stability, while eliminating some of the traditional and inferior methods of lateral support, such as flying buttresses. This is accomplished by using two layers of decking in opposite oblique angles, as opposed to the typical one layer method installed transversely or longitudinally. This idea is found to be unobvious to those skilled in the art due to the bending modulus which in practice allows two layers of a given material to bend more than one layer of equal thickness. To correct for this extra bending the decking can be made thicker or the cross members can be closer together. This would typically use no more material than a bridge decked in the conventional style, due to the elimination of the former methods of diagonal bracing, resulting in a bridge that is 400%-800% stronger laterally.

SUMMARY, RAMIFICATIONS, AND SCOPE

Accordingly, the reader will see that the two layer diagonal decking described in this patent application is a novel and unobvious method of rectifying a long standing problem plaguing timber bridges for centuries, with surprising test results, thus creating the strongest traditional timber bridge available while using approximately the same amount of wood. Not only is it unobvious due to the bending modulus previously mentioned, but there is substantial additional labor involved in this process, which also makes it unobvious to those skilled in the art, especially in former times when the wood had to be cut by hand without the use of modern power tools. However, this extra labor is a good value to the bridge builder when compared to the decreased likelihood of catastrophic failure, and the value of wood in the current economy.

Other ramifications of this process of bridge decking include, and are not limited to, creating bridges ridged enough to be lifted by a crane, or flown into remote locations by helicopter. 

1. A method of decking wooden bridges for pedestrian and vehicular use that substantially increases lateral strength, and therefore overall strength, comprising: (a) a first layer of decking fastened to bridge support members in an oblique angle to said bridge support members, (b) a second layer of decking installed on top of said first layer in an opposite oblique angle to said first layer and fastened through said first layer to said bridge support members, whereby substantially increasing lateral strength of said bridge, hence rendering entire said bridge stronger and more resistant to catastrophic failure, such as, but not limited to those caused by flood, wind, earthquake. 